A week (or month, or year) is not just a quantity of days; we think of new weeks (months, years) as starting on particular days. So Calendar mode provides commands to move to the beginning or end of the week, month or year:
calendar-beginning-of-week).
calendar-end-of-week).
calendar-beginning-of-month).
calendar-end-of-month).
calendar-beginning-of-year).
calendar-end-of-year).
These commands also take numeric arguments as repeat counts, with the repeat count indicating how many weeks, months, or years to move backward or forward.